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Control of fingertip forces in multidigit manipulation
J R Flanagan1, M K Burstedt, R S Johansson
1Department of Psychology, Queen's University, Kingston, Ontario K7L 3N6, Canada.
Journal of Neurophysiology
|April 14, 1999
Summary
Skilled manipulation with three digits, like lifting an object, shows coordinated fingertip forces similar to two-digit tasks. This study reveals new insights into multidigit force control and grasp stability.
Area of Science:
- Neuroscience
- Biomechanics
- Human Motor Control
Background:
- Previous research on fingertip force control primarily examined two-digit manipulation.
- Skilled manipulation involves complex coordination of multiple digits for object interaction.
Purpose of the Study:
- To investigate fingertip force control during a multidigit (three-digit) object lifting task.
- To compare force coordination in three-digit grasps with existing two-digit manipulation studies.
Main Methods:
- Subjects lifted a cylindrical object using a three-digit grip (thumb and two fingers).
- Measured three-dimensional forces, torques, and contact positions for each digit.
- Recorded object's position and orientation during lifting.
Main Results:
- Vertical fingertip forces were synchronized across digits and scaled with object properties.
- Digits applied normal forces that increased with local tangential load, ensuring grasp stability.
- Subjects minimized fingertip forces and avoided horizontal forces while maintaining stability, with subtle adjustments in force distribution and object tilt.
Conclusions:
- Three-digit object lifting exhibits force coordination principles consistent with two-digit grasps.
- Multidigit manipulation introduces unique force control strategies not observed in simpler tasks.
- The motor system balances force minimization with grasp stability in complex manipulation.